1. Field of the Invention
The present invention relates to a medical ultrasonic imaging apparatus, and more particularly relates to optimization of parameters for frequency compound imaging.
2. Description of the Related Art
Compounding smoothes speckles by averaging and adding signals in a plurality of directions to improve quality of vision of a minute contrast difference in an image. Particularly, in frequency compound imaging, a low frequency component and a high frequency component are subjected to signal processing, and added to thereby improve azimuth resolution itself and uniformity of resolution over an image of interest.
Regarding the conventional frequency compound imaging, there is disclosed a study of a quantitative evaluation method of an amount of speckle reduction (William F. W. et al, The Application of K-Space in Pulse Echo Ultrasound, IEEE Transactions on Ultrasound 45(3), 541-558 (1998)). Moreover, there is disclosed a study to clarify relationship between a frequency-band division method and an amount of speckle reduction in the case of two divisions (H. E. Melton, Jr. and P. A. Magnin, A-Mode Speckle Reduction with Compound Frequencies and Compound Bandwidths, Ultrasonic Imaging, 159-173 (1984)). Further, a method is disclosed in which the number of divided frequency bands is about two to five and center frequencies and coefficients are continuously changed according to their depths to keep continuity of quality (Japanese Patent Application Publication No. 2001-184677). Furthermore, a method is disclosed in which, in order to suppress a reduction in distance resolution having a tradeoff relation with an amount of speckle reduction, not only a narrowband signal but also a wideband signal containing the narrowband signal are changed to divided signals (Japanese Patent Application Publication No. 2001-170049).